| 释义 |
‖ rachis|ˈreɪkɪs|
Also rha-. Pl. rachides |ˈreɪkɪdiːz|.
[mod.L., a. Gr. ῥάχις spine, ridge, rib (of a leaf), etc. The more precise spelling rhachis is chiefly confined to sense 2. The pl. rachides is erroneous, as the stem of ῥάχις is not ῥαχιδ- but ῥαχι-.]
1. Bot.
a. The axis of an inflorescence in which flower-stalks occur at short intervals from each other, as in grasses.
1785Martyn Rousseau's Bot. xiii. (1794) 146 The teeth of the rachis or receptacle of the spike bearded. 1830Lindley Nat. Syst. Bot. 258 Terminal flowers sessile upon a 2- or 3-branched rachis. 1861S. Thomson Wild Fl. ii. (ed. 4) 132 The grass blossoms are arranged upon a central stem or rachis. 1875Bennett & Dyer tr. Sachs' Bot. 544 The ebracteate flowers stand on the rachis of the inflorescence.
b. The axis of a pinnately compound leaf or frond, corresponding to the midrib of a simple leaf.
1832Lindley Introd. Bot. i. ii. 107 The term rachis is applied by Willdenow and others..to the petiole and costa of Ferns. 1861Miss Pratt Flower. Pl. VI. 139 The stalk [of fern] is often called the rachis, but strictly speaking, it is composed of two parts. That part which bears the green leaf is the rachis. 1880C. & F. Darwin Movem. Pl. 86 The rachis of the bracken fern..rises above ground under the form of an arch.
2. Anat. The vertebral column, or the primitive cord from which it develops.
1842Brande Dict., Rachis, a term applied by Illiger and other zoologists to the vertebral column of mammals and birds. 1878Bell Gegenbaur's Comp. Anat. 428 The separation of the rachis into skull and vertebral column is not completely effected in Amphioxus.
b. The median part of the odontophore of a mollusc, resembling a series of vertebræ.
1851Woodward Mollusca iv. 27 The tongue, or lingual ribbon, usually forms a triple band, of which the central part is called the rachis. 1866Tate Brit. Mollusks iii. 50 The central area is called the rachis, and the teeth form usually a single series.
c. A cord of protoplasmic matter in the ovary of nematoid worms, round which ova are developed.
1877Huxley Anat. Inv. Anim. xi. 640 An axile cord of protoplasmic substance—the rhachis—and peripheral masses, each..connected by a stalk with the rhachis.
3. Ornith. The stem or shaft of a feather, especially the part bearing the vexillum, as distinguished from the quill.
1874Coues Birds N.W. 607 The central pair..form an angle of 45° with the rachis. Ibid. 616 Rhachides of the first two or three primaries pure white. 1893Newton Dict. Birds 245 In Casuarius each primitive feather consists of a long and slender rhachis bearing two series of rami. |